A “clean room” is a confined area with a carefully controlled environment and highly restricted access in which the air and all surfaces are kept extremely clean. Clean rooms are used to operate highly sensitive machines, to assemble sensitive equipment such as integrated circuit chips, and to perform other delicate operations which can be compromised by minute quantities of dust, moisture, or other contaminants. Clean rooms are designed to attain differing “classes” of cleanliness, suited to particular applications. The “class” of the clean room defines the maximum number of particles of 0.3 micron size or larger that may exist in one cubic foot of space anywhere in the clean room. For example, a “Class 1” clean room may have only one such particle per cubic foot of space.
Clean room lighting involves a number of challenges. For example, Class 1 clean room lighting fixtures must be recessed within the clean room's ventilated ceiling structure without leaving any particle-entrapping protrusions. Such recessing must not interfere with the ceiling-mounted ventilation equipment which maintains the ceiling-to-floor laminar airflow required to ensure that any particles are carried immediately to the clean room floor vents for removal from the clean room. Due to the presence of the ventilation equipment, there is comparatively little clean room ceiling space within which light fixtures can be recessed without interfering with the ventilation equipment.
Conventionally, clean rooms are illuminated by recessing small diameter fluorescent tubes into whatever space remains within the ceiling after installation of the ventilation equipment. There are several drawbacks to this approach. For example, the fluorescent tubes burn out and must be replaced. Since most clean rooms operate 24 hours per day 7 days per week, and since the fluorescent tube replacement procedure compromises the clean room operational environment, burned out tubes are commonly left in place until the clean room is shut down for annual relamping, at which time all of the fluorescent tubes are replaced whether they are burned out or not. Besides necessitating an expensive shutdown of the clean room, the annual relamping procedure is time-consuming and expensive in its own right.
This invention addresses the foregoing drawbacks with the aid of solid state lighting devices which have significantly longer lifetimes than fluorescent tubes and no breakable glass parts, which can pose a significant clean room contaminant hazard. Solid state lighting devices can also be more than easily configured to produce ultraviolet-free light than fluorescent tubes. Such light is desirable in clean rooms used for lithographic production of integrated circuits.